I. Field of the Invention
The present invention relates to techniques of analysis, particularly of hydrocarbon and substituted hydrocarbon mixtures, generally classified in U.S. Class 250.
II. Description of the Prior Art
Many prior teachings of the determination of the individual components of paraffins, isoparaffins, aromatics, napthenes, and olefins (PIANO) have been taught in prior literature and patents. A preferred prior technique is gas chromatography, wherein a sample is injected into an absorbant column swept by an elutriating inert gas, e.g. helium, and the elapsed time for arrival at the end of the column is measured for each of the components, e.g. by a flame ionization detector, thermal conductivity detector, or other detector.
Conventionally, the percents of each of the individual compounds detected by gas chromatography are grouped under their respective generic classifications in the PIANO classification system, and the relative percentage of each of the components paraffins through olefins is determined in weight percent, volume percent, or mole percent as required. An example of this procedure is that taught by Analytical Automation Specialists, Inc., "The Detailed Analysis of Petroleum Naphthas, Reformates, Gasoline and Condensates by High-Resolution Gas Chromatography", Operators Manual, P.O. Box 80653, Baton Rouge, La. 70898. Also available in AAS (Analytical Automated Systems) PIANO Software Package, Sievers Research PIANO Software Package.
Recently, near-infrared (NIR) spectrophotometric analysis has been used to determine baking quality of flour, digestibility of forages, and other physical properties of samples, e.g. in U.S. Pat. No. 4,800,279 to Hieftje, Honigs, and Hirschfeld, and a number of the references cited therein.
Other NIR analysis techniques are taught in J. Prakt. Chem., 317(1), 1-16 by Bernhard and Berthold, who perform structural group analysis of mixtures of saturated and aromatic hydrocarbons, and in the quantitative analysis of benzene-toluene-paraffin mixtures in the near-infrared by Leimer and Schmidt in Chem. Tech. (Leipzig), 25(2), 99-100.
Near-infrared spectroscopy of hydrocarbon functional groups was performed by Tosi and Pinto, Spectrochim ACTA, Part A, 28(3), 585-97, who examined 50 linear and branched paraffins and related the absorbtivities to the concentration of the groups such as CH.sub.3 and CH.sub.2.
Ultraviolet and Near-infrared analysis of mixtures of aromatics is taught by Schmidt in Erdoelkohle, Erdgas, Petrochem., 21(6), 334-40, who sought to determine concentration of specific compounds, not the groups (aromatic, etc.) measured by this invention, and used different wavelengths.
Kelly, Barlow, Jinguji and Callis of the University of Washington, Seattle, (Analytical Chem. 61, 313-320,) found gasoline octane numbers could be predicted from near infrared absorbance in the range 660-1215 nanometers (nm). They found best correlation between absorbance and octane number to occur at 896, 932 and 1164 nm for research octane number, 930, 940 and 1012 nm for motor octane number, and 896, 932 and 1032 nm for pump octane number. Kelly does not teach PIANO analysis, and only uses the short wavelength near-infrared, 660-1220 run, but did determine the aromatic, olefin, and saturate (paraffins plus isoparaffin) content of gasolines. However, Kelly used a very limited number of samples (nine) and restricted their measurements to the short wavelength near infrared (660-1220 nm), unlike the present invention. Furthermore, they did not disclose which wavelengths correlated with aromatic, olefin, or saturate concentrations. Example 6 compares this Kelly work. Thus Kelly does not enable one skilled in the art to practice the present invention nor to attain its advantages.
None of above teach PIANO analysis of the more complex mixtures routinely encountered in petroleum refineries. Such mixtures almost always contain both aromatics and olefins which are generally thought to have overlapping absorbance wavelengths in the mid-infrared region, suggesting that their overtones and combination bands in the near-infrared region would also overlap, and preclude determination of their individual concentrations in the mixtures.
Such mixtures are often very complex; gasoline mixtures frequently contain over 300 compounds.
Also, individual molecular groups found (e.g. methylene) in napthenes, are also found in paraffins and also in isoparaffins, as well as in substituted aromatic compounds, and also in olefins, further compounding the difficulty of analyzing for concentration of individual PIANO components.